Generally, the water pressure transfer method is a method for floating on a water surface in a transfer tub a transfer film formed by applying a predetermined print pattern of non-water solubility on a water-soluble film of polyvinyl alcohol, making wet the water-soluble film of the transfer film with water, immersing an article (an object to be pattern-transferred) into the water in the transfer tub while contacting the transfer film, and transferring the print pattern of the transfer film on a surface of the article using the water pressure generated when the article is immersed into water to form a print layer.
In this water pressure transfer method, although the transfer film is obtained by printing the print pattern on the water-soluble film by gravure printing method etc., this transfer film is generally supplied to the water pressure transfer operation site by being shipped in a roll state after the ink of the print pattern is dried.
The transfer film has a whole outer surface pattern fixture layer in order to make stable the ink pattern on the polyvinyl alcohol of the water soluble film when the water soluble film is made wet or dissolved. Although the whole outer surface pattern fixture layer will be described later in details, the whole outer surface pattern fixture layer of transparent or translucent ink is applied on the whole surface of the transfer film so that the whole area has a uniform thickness in spite of the no ink area and the ink area of color ink layer of the print pattern partially having the visible surface (substrate surface) of the article, that is the print pattern partially having no color ink resulting in having the print pattern partially removed. The whole outer surface pattern fixture layer serves to prevent the print pattern from being unable to be fixed as the polyvinyl alcohol of the water soluble film swells or is dissolved if there is no whole outer surface pattern fixture layer. This whole outer surface pattern fixture layer also serves to prevent the water soluble film from unstably swelling or being dissolved due to the difference between the thicknesses of the area of ink layer and the area of no ink. Thus, this whole outer surface pattern fixture layer is indispensable for the transfer layer for obtaining the desired design.
The water pressure transfer is performed for the purpose of decorating the surface of the article which is the object to be pattern-transferred. However, lately, a cubic effect is required to be imparted to the surface of the article together with the decoration of the article. To comply with this requirement, various unevenness imparting arts have been conventionally adopted (see Patent Documents 1 through 4).
For the conventional unevenness imparting arts, there has been a first conventional prior art in which the unevenness is imparted by printing a pattern on a fine uneven surface of a decorative sheet having the fine uneven surface formed beforehand (see Patent Document 1), a second prior art in which wood flour is mixed into an ink layer etc. of a print pattern of a transfer film to give a fine unevenness to the surface of the water pressure transfer article (see Patent Document 2) or a third prior art in which a fine unevenness is formed on the surface of the article with a base coat layer having an surface unevenness applied to the article before the transfer of the print pattern or a topcoat having variant unevenness formed by a press-molding machine etc. after the transfer, but before hardening the print pattern (see Patent Documents 3).
However, the methods according to these prior arts have the disadvantages that the separate steps such as an emboss process for the decorative sheet (the first prior art) and mechanically imparting the unevenness to the base coat or topcoat (the third prior art) are required and there are the difficulties of obtaining the unevenness other than dot-like one (the second prior art) and the stripe-like unevenness pattern such as wooden skin. Furthermore, none of the prior arts forms the three-dimensional fine unevenness on the print pattern itself and therefore the real tactile feeling of unevenness cannot be obtained.
The applicant has proposed a water pressure transfer method adapted to form the three-dimensional fine unevenness on the print pattern itself without any particular step and to thereby obtain the real tactile feeling of unevenness (Japanese Patent Application No. 2007-277501 of the Patent Document No. 5)
The water pressure transfer method according to the applicant's proposal is a method in which there is prepared a transfer film having a print pattern including a first area of an ink layer and a second area of no ink layer or an ink layer thinner than that of the first area and having no whole outer surface pattern fixture layer, there is formed activating agent convex collection portions by protruding on a surface of an article a surplus portion of the activating agent which is applied onto the surface of the transfer film to activate the ink of the first area while the surplus portion of the activating agent is collected in the second area by being pushed by the surface of the article on the water pressure transfer and there is shrunk the activating agent convex collection portion when the print pattern on the article is hardened whereby an ink print portion corresponding to the second area projects over an ink print portion corresponding to the first area to thereby impart a three-dimensional unevenness shape to the surface of the article surface.
In this new water pressure transfer method, in order to form the activating agent convex collection portions in the second area, the activating agent convex collection portions may be formed by collecting in a convex manner in the second area by a repelling function of the ink layer of the first area and a collection power of the activating agent the surplus portion of the activating agent within the first area. In this case, the collection of the surplus portion of the activating agent may be carried out by setting an interfacial tension of the ink relative to the activating agent in the first and second areas so that the activating agent collection power in the second area acts more greatly than a power for the ink layer of the first area to draw the activating agent and setting the interfacial tension may be carried out so that the interfacial tension relative to the activating agent in the first area gets lower than the interfacial tension relative to the activating agent in the second area. What is meant by “the repelling function” in this specification is the phenomena where the surplus portion of the activating agent remaining on the ink after the activating agent permeates the ink composite until the activating agent is wholly united with the ink composite is pulled from the surface of the portions having the ink layer near the surface of the portions having no ink layer due to the difference of the polarities of the surface of the portions having the ink layer and the surface of the portion having no ink layer. Thus, “the repelling function” never prevents the activating agent from permeating the ink layer.
The activating agent to be used for this new water pressure transfer method is not an organic solvent, but may preferably be one formed of ultraviolet ray hardening resin composite. The activating agent of ultraviolet ray hardening resin has the ultraviolet ray hardening resin component permeated into the ink of the print pattern to activate the dried ink and also hardened by ultraviolet ray in the ink to impart a mechanical and chemical surface protection function to the surface decorative layer formed of the print pattern transferred onto the surface of the article.
The applicant has also proposed an activating agent of ultraviolet ray hardening resin composite suitable for being used in the water pressure transfer (see Patent Document 4). This activating agent includes no organic solvent and includes at least photo-polymerization pre-polymer (photo-polymerization oligomer), photo-polymerization monomer and photo-polymerization initiator. The photo-polymerization pre-polymer may be of 9 to 40 mass %, the photo-polymerization monomer may be of 50 to 90 mass %, the photo-polymerization initiator may be of 0.5 to 5 mass % and the balance may be of 0.5 to 5 mass %. This may have the viscosity of 10 to 100 CPS (25° C.) and the ink solubility of 10 or more at the SP value.
The photo-polymerization monomer of the ultraviolet ray hardening resin component has a solvent power to an ink of the print pattern as well as that to the photo-polymerization pre-polymer, a higher hardenability, a good adhesion to ABS resins, PC materials, etc., which are base materials onto which the print pattern is to be transferred under water pressure, a lower shrinkage when hardened and a good smoothness and also has a good transparency maintained. Thus, the adhesion of the dried and cured print pattern of the water pressure transfer film can be positively recovered by the proper viscosity and ink solubility of the ultraviolet ray hardening resin composite and since the ultraviolet ray hardening resin composite permeates and penetrates the whole thickness of the print pattern from the surface on the side of application of the ultraviolet ray hardening resin composite to the surface on the opposite side so that the print pattern and the ultraviolet ray hardening resin composite are integrally combined with each other over the whole of the print pattern (the whole areas and the whole thickness thereof), the decorative layer obtained by the print pattern transferred on the article is hardened by the ultraviolet ray all over the decorative layer including the outer surface and therefore the print pattern can be solidly attached on the surface of the article and in addition thereto the surface protection function according to the ultraviolet ray hardening can be imparted to the decorative layer itself. Thus, the decorative layer obtained by transferring the print pattern is hardened all over the whole including the outer surface thereof whereby the print pattern can be positively adhered to the surface of the article and in addition thereto, the surface protection function by ultraviolet ray hardening is imparted to the decorative layer itself.
The particular viscosity of 10 to 100 CPS (25° C.) and the particular ink solubility of 10 or more at the SP value of the ultraviolet ray hardening resin composite are the values necessary for making the solubility of the ultraviolet ray hardening resin composite closer to that of the ink component of the print pattern and the particular viscosity of the ultraviolet ray hardening resin composite is the value necessary for maintaining the smoother coating to the ink component of the print pattern and the permeability of the ultraviolet ray hardening resin composite into the ink component.
Furthermore, the particular viscosity of 3 to 30 CPS (25° C.) and the particular ink solubility of 9 or more at the SP value reduces the viscosity of the photo-polymerization pre-polymer having a tendency of high viscosity and also makes the solubility of the ultraviolet ray hardening resin composite closer to that of the ink component of the print pattern. Therefore, there can be obtained the ultraviolet ray hardening resin composite maintaining the property of smoothly applying the ultraviolet ray hardening resin composite on the ink component of the print pattern (smooth applicability) and the property in which the ultraviolet ray hardening resin composite can permeate the ink component in a good manner (permeability). In addition thereto, the ultraviolet ray hardening resin composite has a good adhesion to the ABS resins, the PC materials etc. of the base materials and maintains the smoothness and the transparency when hardened.
In the new water pressure transfer method for imparting a tactile feeling of cubic unevenness by the convex collection portions of the activating agent, in order to enlarge the difference of height between the convex collection portions of the activating agent and the recesses around the convex collection portions, the blend ratio of the photo-polymerization monomer having the high volume shrinkage ratio is required to be 70% or more, for example. However, such a high volume shrinkage ratio reduces the blend ratio of the photo-polymerization pre-polymer, the component to be a main frame of the activating agent, which influences a membrane performance (abrasion resistance and chemical resistance) after hardened with the result that the membrane performance is disadvantageously reduced. Thus, if the activating agent of the ultraviolet ray hardening resin composite previously proposed by the applicant is used for the new water pressure transfer method, the product having the large height difference of the unevenness can be obtained, but sufficient membrane performance cannot be obtained and therefore both of the good tactile feeling of unevenness and the good membrane performance cannot be obtained.
If the blend ratio of the photo-polymerization pre-polymer of the activating agent is so set to be slightly higher in order to heighten the membrane performance of the decorative layer, then the product having the large height difference of unevenness cannot be obtained due to the volume shrinkage ratio of the photo-polymerization pre-polymer less than that of the photo-polymerization polymer and therefore this is undesirable.
On the other hand, since the article with the unevenness to be imparted thereto is a transfer article requiring the tactile feeling of unevenness, there is much considered the chemical resistance against oleic acid used for evaluating the prevention of dirt on the surface of the product due to tactile by a human body. More particularly, as one of the evaluation of the performance of the chemical resistance required for such a transfer article, it is very important that there is evaluated the prevention of dirt due to sweat or remains of a fingerprint of a human body by oleic acid included in the sweat or skin fat of the human body. Thus the resistance to oleic acid is an important performance for the article having the unevenness imparted thereto. Thus, even if there are the ability of forming the unevenness and adjusting the height thereof, the performance of the product is insufficient (or poor). In this manner, if the unevenness tries to be imparted by the new water pressure transfer using the activating agent of prior art disclosed in the Patent Document 4, the membrane performance will be considerably reduced as the smoothness is reduced for obtaining the unevenness. Thus, since the unevenness cannot be imparted in a totally balanced manner in addition to the coating performance, permeability and so on.
Another important problem of the invention is to be able to stably maintain the pattern of the print pattern layer on water even though the transfer film has no whole outer surface pattern fixture layer. As the activating agent of prior art according to the Patent Document 4 is applied onto the transfer film having no whole outer surface pattern fixture layer, the stability of the pattern of the print pattern layer is not sufficient.
For the aforementioned reason, it is never desirable that the water pressure transfer is carried out by using the activating agent of the Patent Document 4 previously proposed by the applicant so that the large height difference is imparted to the surface of the article.